raco ctools docs: improve xref docs and mention "cext-lib" package

pkgs/racket-doc/scribblings/inside/embedding.scrbl

@@ -224,7 +224,7 @@ int main(int argc, char *argv[])
 
 If modules embedded in the executable need to access runtime files
 (via @racketmodname[racket/runtime-path] forms), supply the
-@DFlag{runtime} flag to @exec{raco ctool}, specifying a directory
+@DFlag{runtime} flag to @seclink["ctool" #:doc raco-doc]{@exec{raco ctool}}, specifying a directory
 where the runtime files are to be gathered. The modules in the
 generated @filepath{.c} file will then refer to the files in that
 directory; the directory is normally specified relative to the
@@ -296,10 +296,10 @@ For Racket 3m, an embedding application must call @cpp{scheme_main_setup}
 with a non-zero first argument.
 
 The simple embedding program from the previous section can be
-processed by @exec{raco ctool --xform}, then compiled and linked with
-Racket 3m.  Alternately, the source code can be extended to work with
-either CGC or 3m depending on whether @cpp{MZ_PRECISE_GC} is defined
-on the compiler's command line:
+processed by  @seclink["cc" #:doc raco-doc]{@exec{raco ctool --xform}}, then compiled
+and linked with Racket 3m. Alternately, the source code can be
+extended to work with either CGC or 3m depending on whether
+@cpp{MZ_PRECISE_GC} is defined on the compiler's command line:
 
 @verbatim[#:indent 2]{
 #include "scheme.h"

pkgs/racket-doc/scribblings/raco/c-mods.scrbl

@@ -5,6 +5,9 @@
 
 @title[#:tag "c-mods"]{Embedding Modules via C}
 
+@margin-note{@exec{raco ctool} is provided by the @filepath{cext-lib}
+                package.}
+
 The @DFlag{c-mods} mode for @exec{raco ctool} takes a set of Racket
 modules and generates a C source file that can be used as part of
 program that embeds the Racket run-time system. See @secref[#:doc

pkgs/racket-doc/scribblings/raco/cc.scrbl

@@ -22,6 +22,9 @@ relative to @racket[_file].
 
 For information on writing extensions, see @other-manual[inside-doc].
 
+@margin-note{@exec{raco ctool} is provided by the @filepath{cext-lib}
+              package.}
+    
 Three @exec{raco ctool} modes help for building extensions:
 
 @itemize[